But before you ask... (Finding Service Manuals - a work in progress)

JFGI

Google it (seriously).

If the part has part numbers on it, then Google them. Try removing letters from each end one by one.

It is amazing how often the details of someone's query is satisfied by the first result Google brings up after typing in exactly what the person asked for information about.

Quite frankly, I have better things to do than operate Google for you, and it will be a lot faster if you do it yourself.

How to search

There are many places to search, but here are a few that I have found useful.

Read the Google one even if you're an avid Googler. It has information about extracting searchable stuff from a long part number.

If you have a partial ID on a chip, you may have to do some detective work. Partial numbers are often found on small devices where there's no room to print the whole number. Surface mount components often have code numbers instead of part numbers. Somewhere I will put in a "Partial and Code number search"

Google

Best first stop. But sometimes what you search for results in nothing...

For example a (fictitious) part labelled MTSN74LS244ACXV does not appear in Google. But if one were to remove some of the letters from each end and search for SN74LS244A, you'd find it.

But how do you know what letters and numbers to remove?

Often the initial letters define the manufacturer, and he same part can be manufactured by a number of companies. Here is a list of such prefixes (note that it's not exhaustive). If you recognise one of these prefixes, it's usually best to remove anything that might appear before it. Sometimes it is best to remove it too.

The suffixes describe lots of things, like:
* Temperature ranges
* Tolerance
* Packaging (e.g. DIL or SMD)
* Packaging (e.g. came on a reel, or in a tube, etc.)
* Revision number
* Voltage rating
...and much more.

Frequently you will have to remove quite a bit of it (especially if working from a full manufacturers part number) to get something that Google will find. You can add a * at the end of the search term to find things beginning with that, so a search for SN74129* will find hits where there are various suffixes.

Once you have found some hits, look for images and descriptions that seem to indicate a similar part. For example, if it's a transformer, ignore stuff relating to swimming pool pumps and reels of cable. If you removed a lot of prefix or suffix all at once, you might try adding some back, one character at a time.

If the only way to get any hits is to pare down the number to something that is quite generic (you will know this because you get lots of hits for totally unrelated stuff) then you can try adding "datasheet", or if it's a transformer, add "transformer".

Even if you're looking for a datasheet, I would not add "datasheet" to the first search. All this does is bring up a bazzilion sites that want you to pay them for datasheets. Sure, you might eventually have to go down that route, but try for a free one first (because almost all datasheets are available free.

Ideally you will have found your way to a site that sells the item, has some in stock, and provides a datasheet.

But maybe not.

AllDatasheet
...And Davenn reminds me about AllDatasheet.com, another site you'll be aware of if you've done any googling for datasheets. It also has its own search, but I must admit to never having used it.

AllTransistors.com
This site allows searching and datasheet retrieval, *and* has SMD codes. Transistors only, but well worth looking up if your unknown part is a transistor. Here. (Thanks to grant1842)

ChipDocs
ChipDocs is a site that asks you to pay for datasheets. If they have what you want, and you are being paid to find datasheets (i.e. it's for work) then $US95 for a year's access might be good value. I don't know, I've never paid. But I do occasionally use them because they do list (free) the chip names for which they have documentation. This can be very useful if you're searching on a partial name (the full name may not be printed on the device itself). This additional information may be useful in using another (free) site to locate a datasheet.

ChipFind
I seem to always forget ChipFind. It's in the .ru domain, and I'm always careful when I stray in there, but this part of the site is in English, and I have yet to download a duff pdf. For some reason Google doesn't show them up, but I have found them to be useful.

Ciiva

ciiva for descriptive search when you are not sure of part number and only have some keywords
Thanks Lemanlake

DatasheetCatalog

Makerdino reminded me about datasheetcatalog.com. I often find links to stuff here, via Google, but you can go straight to their home page and search. If there are several alternate sources for a part, it will often list them by manufacturer.

Datasheet Archive

As Electrobrains points out the similarly named datasheet archive is another good source.

These three (Datasheet Catalog, All Datasheet, and Datasheet Archive) are similr enough that you may have seen two or more of them and not noticed they were different... They do have access to different datasheets, but I mostly find my way to them via Google.

FindChips

If it is an electronic component, my next search after Google would be findchips. This is a bit like Google in operation, but simpler. Just put the part number in. It will search a stack of places that sell electronic components and give you a list of results. You may need to do the same sort of fiddling with the part number as you do with Google (except that a * on the end isn't needed). This site can find stuff that Google can't (and vice versa).

Findchips returns (an often abbreviated) list of results from the various sites it searches.

Beware that the search results may indicate pricing or stock levels that are out of date. Click through if this is important!

Octopart

Makerdino also reminded me about octopart.com. This is a bit of a cross between DatasheetCatalog and FindChips. It finds suppliers and gives links to datasheets.

The results it offers from its own search lead you to arguably better information than you get as links into this site from Google. So searching from this site is actually a good idea. (Thanks Makerdino)


Decoding the resistor and capacitor codes


A page with the standard resistor values

Capacitor codes


Military Devices

The US Military have an online cross-reference available here. (Thanks to shrtrnd)

Databooks

If you have access to databooks (which are essentially a collection of related datasheets) then these can be a useful tool. Old databooks are useful because they potentially list obsolete devices for which the datasheets may be hard to obtain.

This guy has a set of old Motorola and On Semiconductor databooks.

This gut has a complete Motorola selection guide (comprises a set of selection guides). He also has a large number of datasheets from several other manufacturers

Murata has a lot of catalogs with data on the components:
https://www.murata.com/en-global/support/library/catalog

Bitsavers has a large archive of old databooks and datasheets:
http://bitsavers.org/components/

Tubebooks.org
Tubebooks.org has a lot of tubes / valves data books:

More tubes can be found on the site of nj7p:

When you are looking for more data on vacuum tubes, have a look at this site:
https://frank.pocnet.net/index.html

Cross reference lists
http://matthieu.benoit.free.fr/cross.htm

Manufacturers web sites

It pays to search manufacturers web sites (if you know a possible manufacturer) as sometimes their information is hidden from Google.

I have found that (if a part is old) you may be advised to try to find notices the manufacturer put out regarding the part's end of life. Sometimes this can indicate an alternative part.

HP part numbers

Hewlett Packard placed their own part numbers on many components. It can be difficult finding what those parts are.

Here is a list of HP part numbers cross-referenced to normal (commercial) part numbers. (Thanks also to shrtrnd)

You might like to check out this page too.

Tektronics

Tektronics also have their own part numbers.

Here is a cross-reference between their part numbers and commercial part numbers. (Thanks again to shrtrnd)

Repeater-Builder
A site that has information on a number of miscellaneous (mostly communications related) hardware is Repeater-Builder..

PINOUTS.RU
Another site in the Russian TLD. Pinouts.ru provides the pinouts to many devices, cables, terminators, etc. Very worth while if you cant figure out the interface to something.
Tubes
Here is a site with datasheets for valves.
Power IC identification
Here is an Iranian site that tries to identify some power devices by the functions of their pins. This is an interesting resource and is coupled to datasheets for the devices. May be helpful if you have an unidentified power device.
Flyback Transformers
Also at the same Iranian site as above, here is a list of flyback transformers.
Partial and Code Number search
Sometimes the full part number doesn't appear on a device.
Japanese semiconductors do this all the time. For example a three legged device having C123 on it will be a 2SC123. The first number is one less than the number of legs (I think that's the rule!) and the second is always an S.
I have found ChipDocs (see above) to be quite good at searching on partial number matches. The list of parts it provides may be useful, even if you don't want to pay them for access to the datasheet.
Surface mount devices can have one of several things written on them:
* Nothing
* Value (or value code)
* Part number (perhaps partial)
* Code number
You're on your own with the first two
The last one requires that you have a document cross-referencing these codes to actual part numbers. Beware that there are far fewer codes than parts, and not all their uses have been documented. It may tell you what you have, or it may give you a few suggestions, or it may lead you astray
Google for "smd code book", or try here, here, or if you want a commercial option here.
The codebooks (look at the second one) have instructions that I do not need to repeat here. Ifhttp://www.electronicspoint.com/but-before-you-ask-work-progress-t228862.html you look at just a simple code "02" you will find that the second option above lists four possibilities, the sample of the commercial one lists four 2-pin devices, and five 3 pin devices. Again, whether you decide to pay for the commercial option depends on your needs.
Another option (as suggested by OLIVE2222) is to google for the package and the observed code. A recent example was a SOT-23-5 package marked "LAC". Googling for "LAC sot23" yielded a sensible result (in this case an ADP3308). Note that there are a number of other devices that are potential matches for this query which are not found by google, but it's still worth a shot.

Service Manuals and Schematics

BAMA
Daddles pointed out the Boat Anchor Manual Archive, I have no idea if this is related in any way to EBAMAN, or if two people decided that these things were boat anchors. This site does not require registration, but also does not have any obvious way to submit material.
Note that the link above is to the mirror site. The mirror says the main site is down. I will try to remember to update this entry if/when it goes online again.

EBAMAN

Davenn is always pushing EBAMAN, and with good reason. This guy has a good selection of old manuals and he doesn't charge for them. I would encourage you to upload to him any manuals you may have in electronic format. You do have to register.

Electrotanya

http://www.elektrotanya.com. This is an excellent site for finding service manuals and technical information .... thanks Kris

KO4BB

Here is another site with a collection of manuals. (Thanks somewhat indirectly to shrtrnd for this also)

ManualOwl

ManualOwl is a site that tries to provide manuals free. Give it a go. Most of what I found were user manuals though

s-manuals.com
A site I've just found is s-manuals.com. As well as service manuals for computers, laptops, printers, etc., it has an easy to use lookup for SMT codes.

Vintage Radio
Vintage Radio Info has a lot of Heathkit schematics and some other stuff:

University of Stuttgard
A lot of old data books and datasheets can be found in the components archive of bitsavers at the University of Stuttgart

 

Thanks